# ScienceNostalgia101

Senior Members

125

## Posts posted by ScienceNostalgia101

1. ### P = nRT/V vs. P=F/A paradox?

Ah, so it's just an approximation, then. That makes more sense of it.

Thanks again.

2. ### P = nRT/V vs. P=F/A paradox?

3 minutes ago, swansont said:

A temperature decrease causing a pressure drop from PV=nRT assumes V and n are constant (or only have small changes) which are probably not good assumptions.

If water condenses out, n will drop. The atmosphere does not have a fixed boundary, so V may effectively be lower. You would have to know the size of those effects to draw a conclusion about P

What if there is less atmosphere?

Ah, the condensation part makes sense, then.

So is phase change of compounds/elements involved the only means by which "n" changes? Or is it also possible for an expanding/contracting/otherwise changing atmosphere to shoot more matter out into space and/or attract more matter from outer space?

And another thing I forgot to consider earlier on, as you mentioned the lack of a fixed boundary... Earth's atmosphere is exponentially decreasing with distance, rather than having any arbitrary "threshold" where Earth ends and space begins. So that raises the question... what would decreasing V be equivalent to in that context? An exponential function with a different base? Different rate of change? Both? Neither?

3. ### A rotating vector field without a zero point?

From my understanding, it is not only possible to have a rotating vector field with a point in its centre where the velocity vector is precisely zero, but that the reasons to expect one follow from the fact that if the surroundings are rotating about one point, they are not moving at that point.

But what if you had a moving vector field? For instance, let's say you had the centre of some galaxy, about which all the stars around it were orbiting, moving through space. Obviously in the reference frame that is that moving galaxy, the velocity of that centre is zero. But in some external reference frame not moving parallel to that galaxy, that centre is not zero. Does there have to be some other point in that galaxy, then, at which the velocity is zero in the other reference frame, or is there some means by which literally no point in that galaxy has a zero point?

Not sure whether this is better suited to the math or physics board; thought I'd put it here since I assume chemistry and geology have used for the math of rotational dynamics as well.

4. ### P = nRT/V vs. P=F/A paradox?

So when Day After Tomorrow came out, a lot of people were saying online that a temperature decrease would, per the ideal gas law, decrease pressure, and that the movie failed to portray the effects of this drawing air out of enclosed surfaces. This summer after noticing the office's alcohol based sanitizer containers dripping from overpressurization the topic has come to mind again.

However, pressure is also proportional to the weight of the air above a given surface. So if the surface area of Earth remains the same, would that not mean the average pressure has to remain the same? Would therefore the volume of the atmosphere contract? (I would assume thermal expansion of liquid/solid interior of the Earth is at a less drastic rate.)

Conversely, real-life climate change is known to increase average global temperatures, which I would presume increases the total volume of the atmosphere. However, it's also known to be more pronounced at the poles than the tropics (I often see this pointed out but I haven't come across anything pointing out why) so would that mean the shape of the atmosphere as well?

This also got me thinking; for the ideal gas law; or some hypothetical differential equivalent thereof; to work at every point in space, that would mean there has to be more volume per unit space where the temperature's higher. Doesn't this suggest the present shape of the atmosphere is actually different than the shape of the Earth? That it would bulge more at the equator than the Earth does, and shrink more at the poles than the Earth does? If climate change expands the atmosphere more rapidly at the poles than the tropics, will this create an atmospheric shape more similar to that of the Earth? (Ie. Larger but more "to scale" than before?)

5. ### Ultraviolet light through a prism...

On 5/8/2020 at 3:14 PM, Strange said:

Yes. (But you would need to find a material for the prism that is transparent to those frequencies; I don't think normal glass is.)

Would a diffraction grating work? I've long been interested in splitting sunlight into its UV and visible rays separately.

6. ### On oxygen consumption/CO2 exhalation by animals

I stand corrected, then. My bad!

7. ### On oxygen consumption/CO2 exhalation by animals

53 minutes ago, MigL said:

Yeah, they once used animal fats as fuel for lamps.
You want to go back to that instead of using electricity ?

What about reducing human population also ?
I find it ironic that AGW will make life difficult, or impossible, for a sizeable fraction of human and animal populations, and your solution is to 'cull' a sizeable fraction of human and animal populations.
Doesn't that defeat the purpose of combatting AGW ?

No. AGW wouldn't just reduce population, but would also cause human suffering in the process. Conversely, the fewer people are born, the higher the quality of life per person, if only for having more natural resources per person, let alone lesser effects on pollution.

But the question of how to get there is still a valid one. The non-coercive market tactic that is the enormous cost of raising a child has slowed birth rates very gradually, but not quickly enough to stop global warming. If we were to force the latter, it would be considered dishonourable to resort to such a coercive tactic.

On top of that, a lot of people see reduced birth rates as a short-sighted solution to the problem anyway; what happens in a few decades' time when Gen Xers retire and there aren't enough tax dollars from newly employed workers born in the 2020s to keep them alive? We could let in more immigrants to stem the tide, but what will that do for countries into which no one born elsewhere wants to set foot?

At least with animals, the solution is clearer, because they didn't have grandparents to look after. Either hunters already killed them all, or other animals did.

A flood is harmful to a person because once the flood arrives, they're living in filth. Animals were living in filth anyway so they had less to live for. For human beings, the day they killed each other in the aftermath of a hurricane was the most important day of their lives. For animals, it was Tuesday.

As such, the alleviation of human suffering should take priority over an animal's life, which would've been taken by another animal if it wasn't by us.

People have backyard fireplaces even though they have indoor lights. I'm sure having some of their light and heat be provided by burning animal fats wouldn't be too unthinkable anyway. (Personally, I kind of like that barbecue scent it creates.)

8. ### At-home chemistry labs

In my early teen years, I loved playing with vinegar and baking soda at home during the summer months, but I hated chemistry labs at school. The crowded, hectic, noisy, structured, time-constrained stressful environment wasn't exactly as charming as a bottle popping in my backyard in the warm summer sun.

And now, the next generation of students is facing a situation where school isn't just stressful, but could be a literal threat to life and limb. We are told the teacher must supervise a student in person when they're carrying out chemistry labs; that doing these at home at a distance would be reckless endangerment.

Well, sending kids to school during a pandemic is also reckless endangerment, so the point is moot.

Is there any way to have parents and/or specialized private tutors sign a contract promising they'll supervise the student when they carry out these chemistry labs instead? We hear of parents struggling to help students with homework, but lab safety is more akin to common sense than to esoteric details, and the great outdoors, so long as the chemicals are downwind, reduces the need for a fume hood. Those who work more quickly no longer have to "find other course work" they can do while waiting for the rest of them to finish up, and the ones who work more slowly won't be feeling the stress of how to handle a paraffin wax candle with the feeling they're holding everyone else back making them more nervous... and possibly more clumsy in the process.

The parents who DO want to help their kids carry out these labs will reduce the burden on the tutoring industry, which can handle the rest, and we might be able to not only keep chemistry labs alive during this pandemic, but create a new model of chemistry lab from which more enjoyment can flourish.

The question of how to document whether the students were actually doing these labs or only pretending to is a real one, but there could be all kinds of potential alternative solutions. My personal favourite would be for parents or tutors to film them, just as an incentive for honesty. We already have video projects in media classes, so if the legitimacy of video evidence for the purposes of school were in doubt, so too would the validity of media class assessment.

But regardless of the supposed flaws of that option, that doesn't mean we need to go back to the old model of doing things, especially during a pandemic.

What say you, Science Forums? Are at-home chemistry labs an option worth exploring? If they aren't, is there any way to have them carried out in a setting other than either "at home" or "at school"?

9. ### On oxygen consumption/CO2 exhalation by animals

When downplaying climate change, people often invoke the fact that CO2 is given off not just by fossil fuels but by breathing as well.

When celebrating others' deaths, people like to say "well, [insert person whose death is being celebrated here] was a waste of oxygen while they were alive anyway."

I don't mean to imply the above come from the same people; in fact, I have no specific example in mind of anyone I can confirm for a fact has definitively said both.

My point is that people seem to be under the impression that the consumption of oxygen to replace with carbon dioxide due also to respiration, rather than just combustion, is significant even among human beings in particular, let alone among animals.

I get the impression that, among human beings, it's a small fraction of total carbon dioxide emissions, and that vehicles give off much more if only by the fact that they are so much heavier and require so much more energy to move than, let's say, a bicycle. Otherwise comparisons between countries on CO2 emissions per capita would be a moot point. But what about the animal kingdom as a whole?

Presumably, prior to humanity's arrival on the scene, the animal kingdom evolved to exhale enough CO2 to provide adequate concentrations thereof for the photosynthesis of plants and phytoplankton. We have increased this concentration, sure, but the threshold often talked about is a "doubling" of CO2 emissions... suggesting that, prior to our arrival, animals accounted for an amount comparable to that which we have since added.

So why, then, couldn't hunting be considered a means of climate control? I don't just mean culling of overpopulated species, (though that obviously has its place) but also hunting of predator and prey alike, at proportional rates, such that we reduce the population of every other species on Earth to a fraction of what it was before, while still keeping the ratios intact? (Ie. Half as many foxes, half as many rabbits, etc...?) Would that not create a massive reduction in atmospheric CO2?

As well, if we ate the creatures we hunted in lieu of farming livestock; or burned the fatty tissue we removed to create lean cuts of meat in lieu of burning fossil fuels; would that not also help reduce CO2 emissions even further?

10. ### Gravity-driven transpotation along a shallow incline

So firefighters, when they need to get to a lower floor in a hurry, slide down a pole. They let gravity to the work, rather than their legs.

I'm kind of left wondering; wouldn't this be a good alternative means of transport, to locations of a lower elevation? Rather than having a bunch of asphalt-paved roads leading from something high-elevation (eg. an airport) to something low-elevation (eg. a seaport) why not have; instead of and/or in addition; a pole or large slide that lets gravity do the work?

Here are my two proposals.

1. A thick metal cylinder, that would be secured on each end, from which customers could put their arms and legs into sleeves attached to rings around the pipe. So long as the force of friction is less than the forward component of gravity pulling them along, would they not reach their destination without the aid of fossil fuels and/or electricity?

2. A large ramp whose top surface is of reduced friction; and/or has a cart on which people can sit, as it too slides along the surface. Assume the second sentence from #1 still applies.

Assume for the purposes of each of the above that safety precautions; such as guard rails for the latter, or spring-loaded protective clothing for either; are available.

11. ### Corona virus general questions mega thread

If wetmarkets create new diseases by having so many different species of animals in close proximity, how come zoos aren't as prone to creating new diseases?

12. ### Corona virus general questions mega thread

Question 1: Would the deliberate germ exposure lifestyle advocated by comedians like George Carlin have made people's immune systems better equipped to deal with diseases like this one? Why or why not?

Question 2: Would a food-delivery equivalent of mass transit; such as, let's say, a large, moving trolley that does curbside delivery of food parcels with recipients' names on them (be it by mechanically tossing them or leaving people to walk by and pick them up) be more likely to spread disease, or less so?

13. ### Implications of movie physics

Technically a TV scene and not a movie scene, but in this Simpsons scene, an avalanche buries a cabin. Homer finds out by opening the door; only for the snow that formed around the cabin to fall inward.

1. Would the snow, once it has buried the cabin, maintain its shape even if an open window or door gives it a new path downward? Or would gravity force the compressed snow to expand again into the cabin?

2. Wouldn't the snow outside look dark from the inside, because of the snow's scattering of sunlight? Is there any formula for light intensity as a function of snow depth?

14. ### Alternative power sources megathread?

Sorry to bump this again, but I have another question; what about waterwheels?

If one lined every river in the USA with height-adjustable waterwheels, would that be a means to convert rivers' kinetic energy into electrical energy? Could they be mass-manufactured cheaply enough to supply the USA's energy needs if one were to put every unemployed American to work manufacturing them?

15. ### Alternative water infrastructure megathread

There are a number of things for which "bacteria-laden, but not salty" water are still useful (farming, spraying on forest fires, etc...) and in some places, like California, far more of the state's clean, treated tapwater goes to such uses than to direct ingestion of said water.

Conversely, I presume there are things for which saltwater could be useful (bathing, spraying oneself with it as an alternative to air conditioning) that bacteria-laden water would not.

So what I'm wondering is... would it be practical to have 2 or 3 different sets of water infrastructure, for 2 or 3 distinct purposes, as an alternative to one single one?

For instance, suppose you had a set of germ-water pipelines; a western equivalent of Chinese tapwater, if you will. Now, I don't know whether the energy Chinese people consume on boiling tapwater to kill pathogens outweighs the energy the west uses to purge it of pathogens, but suppose we had a separate set of pipelines for water that does not need to be germ-free, and only needs to be used for farm irrigation or forest fire extinguishing. Here's one proposal on how to go about that. To summarize, you have a concave-up ellipsoid over the intertropical convergence zone to capture rainwater, and create a pressure head from the accumulation of rain, such that the water doesn't need to be pumped vertically upward. The more specific caveat, for the purposes of this thread, is that the pipelines would be attached to sprinklers both in the forest and in the farms, such that they can be opened manually by farmers, or opened automatically by heat like building sprinklers. Is this practical and/or feasible?

For another, suppose you had a set of saltwater pipelines, piping raw seawater vertically upward, and filtering it to keep animals out, before distributing it to the masses. Now, to be honest, I'm not sure how clean seawater is, or how small a filter you would need; or whether filtration would even be enough, whether for small animals or for microbes. I know people often swim in it, but I'm not sure whether this leaves people cleaner or less clean. Would it be feasible or practical to have a network of saltwater pipelines, whether filtered or unfiltered, for the purposes of bathing, and/or in spraying oneself to keep cool during warm weather? Would this be more energy-efficient than air conditioning, or less?

16. ### Wings without a motor vehicle

I say "without a motor vehicle" because I know there's light aircraft you can get that would cost an amount comparable to a personal motor vehicle. But I'm discussing this; mostly as a thought experiment; as to whether or not there's wings you could attach to your arms and achieve lift by acquiring a high enough speed without a motor vehicle. (Let's say, rolling downhill in roller blades or a skateboard or something like that. Presumably also wearing protective body armor with springs in case anything goes wrong.)

For instance, suppose you had encased your arms in wings designed in a similar shape to airplane wings. What would the scaling effects be? Would the most efficient shape at a small scale be the same shape as the most efficient one at a large scale?

As well, what would the scaling effects be on speed required? Assuming the ratio of wing size to body size was the same as an airplane's wing size to fuselage size, would you need, let's say, only a tenth as much speed at a hundredth as much mass or something like that?

17. ### Paper incineration vs. paper recycling

So from my understanding, paper is mostly just wood pulp, with a few other chemicals added. If trees weren't cut down to make wood, they would die in nature. If they died in nature; they would at best give off carbon dioxide; at worst give off even worse greenhouse gases like methane. (I think it's typically both, with how much of each depending on what kind of decomposers get at it?)

So what's the deal with paper recycling? Why are we even recycling paper at all, when burning it would at worst produce the same end-result as a tree's best-case scenario in nature, and at best could be used as a source of heat energy that reduces combustion of other, less renewable materials?

Is the issue with the fumes from combustion of chemicals in paper? If so does it depend on the paper, and how does that compare to the fumes that would be given off from some recycling truck taking the paper all the way to... wherever it's recycled? And even if it is, why is electricity considered a more efficient way to head a home than, let's say, an old-fashioned wood-stove? Again, the choice is between that tree giving off CO2 in your stove vs. that plus worse gases in nature... why is the latter considered a preferable option?

18. ### Physics of video games

I'm not sure whether this belongs in the physics of movies thread or not, but I figure I should have a spearate thread for video games given the interactive nature of the medium.

In one part of Kaizo Mario 3, Mario is temporarily in projectile motion, until his trajectory crosses paths with a waterfall. At this point, the viscosity of his surroundings is no longer negligible, and therefore, he can push his feet downward against the water to propel himself upward.

I assume it's exaggerated, and that one couldn't possible propel oneself to THAT extent in real life. But at the same time, this leaves me wondering whether it's possible to "slightly" propel oneself this way, or not at all because it violates conservation of momentum. I know in horizontal motion, one can swim by pushing the water back and therefore propelling oneself forward; it's a matter of encountering less water resistance when putting your hands in front of you than when pushing the water behind you. Could the same thing work vertically? Does it depend on whether one positions oneself for it before entering the waterfall or after?

19. ### COVID-19 outbreak (caused by SARS-CoV-2)

On 1/24/2020 at 1:39 PM, CharonY said:

It is one of the issues that are going to be increasingly difficult to contain due to increasing mobility of folks. Right now there are ca. 800 infections and the Chinese government has restricted travel in a possibly unprecedented scale.

It should be noted that this at bets highly speculative. Bats are a suspected reservoir, but nothing is certain yet. A  cooked soup is less likely to be the culprit than direct contact with one. But again, it is not sure whether the virus originated from bats in the first place. It just has similarities to some known to be found in bats.

But is eating bat or snake meat safe so long as it's cooked long enough? Is there any virus or other pathogen that'll be present no matter the temperature to which it is heated or the duration for which it's heated to that temperature?

While I'm at it, I know it's a distinct topic, but... does the same apply to human meat? I'm not considering trying it or anything, but I know a lot of people in desperate circumstances end up resorting to it, is that safe as long as it's heated enough or is there some other reason that's unsafe?

20. ### COVID-19 outbreak (caused by SARS-CoV-2)

Not sure whether this is better for here or Biology, but I'll put it here for now. I assume most of you have already heard of China's coronavirus outbreak, but in case you haven't, a little refresher...

A. So does this suggest doing farming within the city limits of a major city is more likely to spread disease than relegating the farming tasks to small towns? Does it depend on whether it's meat farming or just vegetable farming? Either way, how come China often does their farming in major cities, while in the United States, farming's considered a "small town" thing?

B. Within the idea of farming in cities in particular, is it safer to slaughter animals before bringing them to a market, or after? Does the former risk causing insects and/or microbes to get at them faster or something?

C. Within the latter, is it safer to cook the meat before bringing it to the wet market, or to leave the customer to cook it? Would "cooked" meat have only the illusion of safety since in an open air market insects and/or microbes could get at it?

D. Is there any animal that's dangerous to eat no matter how long you cook it for?

21. ### Alternative power sources megathread?

Another question now (sorry to keep bumping this, but it's not letting me edit the previous post now) but I was wondering another thing.

I mentioned before the question of a concave arrangement of various small mirrors, vs. one large concave mirror, in the context of solar collectors on land. It was pointed out that in that context, it's better to have a number of small mirrors than one large one. Does the same apply to thermal solar power at sea? If one were to mass-manufacture, and then arrange into a concave pattern, a series of small mirrors, could most of the thermal energy that would otherwise fall on the Atlantic Ocean instead be captured by these solar collectors, if they were made to float in the ocean? (Presumably tied to each other and the land, to prevent them from being swept away by the currents...)

22. ### Are acidity and alkalinity conserved quantities?

Looking at various chemical reactions, I used to see parallels in acidity and alkalinity to the energy concept. Acids and bases neutralize; sort of temperatures contrasting. Acids react with metals to form neutral hydrogen and salt; but those metals would if electrolyzed would've become alkaline, so it almost looks like the "alkalinity" equivalent of latent energy. And of course, if you burn plants, the ashes are alkaline, but the gases could be reacted with water to form acids. A divergence between alkalinity and acidity, if you will.

But then I found this.

This person forms a strong acid; hydrochloric acid; by reacting together two substances for which neither of them are strong acids. The other product of this reaction is not a strong base, so it's not a "divergent" reaction either. Is there some sort of "latent" alkalinity contained here? If so, could something like this be used to reverse the effects of acid rain by, let's say, reacting together substances that aren't strong bases to form a strong base, with the other product not being a strong acid, therefore increasing the pH of the bodies of water?

23. ### Alternative power sources megathread?

On 1/17/2020 at 7:35 PM, Sensei said:

I am using my balcony as refrigerator during true winter (hard to get one these days).. After shopping e.g. beers and meat land on my balcony (there is -5 C at the moment).

Before refrigerator has been created people used ice houses

which costed nothing to operate except a while of work to gather ice.

ps. Typical house electronic and electric devices are not designed to operate in cold and/or humid environment..

For the record I wasn't referring to using indoor appliances outdoors so much as whether or not there's some outdoor equivalent that'd still keep it cold on abnormally warm (as far as winter goes) days.

In any case, I was surprised to learn they manage to store ice all year, let alone through the occasional warm day within winter. I guess anything well insulated enough with enough ice in it would prevent the temperature from going too far above freezing, if only by convection. (Though I'd be terrified of accidentally locking myself in one.)

24. ### Alternative power sources megathread?

Can't edit prior post. Have a new energy-saver inquiry.

Is it more energy-efficient, in the wintertime, to have an outdoor refrigerator/freezer, such that the temperature difference between the outdoor air and refrigerator/freezer is less than that between the indoor air and refrigerator/freezer, or less efficient because an indoor refrigerator/freezer releases heat into its surroundings anyway?

25. ### Tree branch smolders; then explodes; from electricity?

Wasn't sure whether this belonged in physics or chemistry, but being that from my familiarity with physics, heat makes objects LESS conductive, I assume it's chemistry that explains this. (And/or gives us enough to go on as to whether or not it's a hoax.)

Starting at 4 minutes and 13 seconds in, you can see a tree branch that fell on two power lines conduct smolder; presumably from conducting electricity between them. However, it takes more than a minute for any flames to become visible. Within seconds of the flame becoming visible, you can hear audible electrical arc sounds for a few seconds before the tree branch outright explodes, turning the smoke given off from grey to brown.

So what's going on here? Does the electricity directly cause chemical reactions that produce compounds more electrically conductive than those of the tree branch itself? Or does the smoldering cause that? As well, why the abrupt shift from flame to explosion if it took more than a minute for flames to appear?

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